1. Technical Field
The present invention generally relates to a power conversion system of a multi-phase generator and a method of operating the same, and more particularly to a parallel-connected power conversion system of a multi-phase generator with a power factor correction function and a method of operating the same.
2. Description of Related Art
At present, the common converters of the power generation system can be roughly divided into two system structures: a passive rectification structure and an active rectification structure. Reference is made to FIG. 1, which is a schematic circuit diagram of a related art power generation system with a passive rectifying converter. The power generation system has a passive full-bridge rectifier 10A electrically coupled to a permanent magnet generator (PMG) 20A. The passive full-bridge rectifier 10A is provided to convert a three-phase AC voltage outputted from the permanent magnet generator 20A into a single-phase DC voltage, and also an inductance element Lmp and a switch element Swp are operated to implement the power conversion. For the power generation system with the passive rectifier, the major advantage thereof is that the overall efficiency is maximal because only one drive switch is switched to achieve the power conversion and the caused conversion losses are very small. Particularly, the smaller power generators or lower wind speed operations are adopted. However, the passive rectifying structure cannot actively control the power factor. Also, the ripple torque coupled from the output ripple current generated from the permanent magnet generator 20A causes vibration and noises because the passive full-bridge rectifier 10A can only obtain peak-voltage energy of the three-phase voltage.
Reference is made to FIG. 2 which is a schematic circuit diagram of a related art power generation system with an active rectifying converter. There are six active switches and three passive inductors installed in a power side converter 70A. In addition, a position detector installed on a rotor of the generator 60A is provided to acquire instantaneous rotation speed and non-fixed frequency and phase. Accordingly, the frequencies with same frequency and phase following the fundamental wave are required for the instantaneous rotation speed control and the SVPWM (space vector PWM) control to complete the power conversion. Further, the full-voltage power can be implemented because the controller used in the active rectifying structure can synchronously provide power conversion followed by the three-phase AC voltage. However, it is unfavorable for controllers to provide power conversion for various permanent magnet generators since the six active switches need to be simultaneously driven to result in complicated controls and larger power losses.
Especially, because of frequent variation in wind speed and wind direction, the wind power is more unstable compared to the electricity power generated from the electric grids. In addition, it is very difficult to implement the power factor control for the unstable power source.
Accordingly, it is desirable to provide a parallel-connected power conversion system of a multi-phase generator and a method of operating the same to overcome difficulty of controlling the power factor for the unstable power source by low-loss and simple-control designs.